How to Read a Head CTHow to Read a Head CT

(or “How I learned to stop worrying and love computed tomography”)

Andrew D. Perron, MD, FACEPAndrew D. Perron, MD, FACEP

EM Residency Program DirectorEM Residency Program Director

Department of Emergency MedicineDepartment of Emergency MedicineMaine Medical CenterMaine Medical Center

Portland, MEPortland, ME

Andrew D. Perron, MD, FACEP

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Head CTHead CT• Has assumed a critical role in the daily

practice of Emergency Medicine for evaluating intracranial emergencies. (e.g. Trauma, Stroke, SAH, ICH).

• Most practitioners have limited experience with interpretation.

• In many situations, the Emergency Physician must initially interpret and acton the CT without specialist assistance.

Andrew D. Perron, MD, FACEP4

Head CTHead CT• Most EM training programs have no

formalized training process to meet this need.

• Many Emergency Physicians are uncomfortable interpreting CTs.

• Studies have shown that EPs have a significant “miss rate” on cranial CT interpretation.

Andrew D. Perron, MD, FACEP5

Head CTHead CT

• In medical school, we are taught a systematic technique to interpret ECGs (rate, rhythm, axis, etc.) so that all aspects are reviewed, and no findings are missed.

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Head CTHead CT

• The intent of this session is to introduce a similar systematic method of cranial CT interpretation, based on the mnemonic…

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Head CTHead CT

“Blood Can Be Very Bad”

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BBlood lood CCan an BBe e VVery ery BBadad

• Blood

• Cisterns

• Brain

• Ventricles

• Bone

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BBlood lood CCan an BBe e VVery ery BBadad

• Blood

• Cisterns

• Brain

• Ventricles

• Bone

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BBlood lood CCan an BBe e VVery ery BBadad

• Blood

• Cisterns

• Brain

• Ventricles

• Bone

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BBlood lood CCan an BBe e VVery ery BBadad

• Blood

• Cisterns

• Brain

• Ventricles

• Bone

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BBlood lood CCan an BBe e VVery ery BBadad

• Blood

• Cisterns

• Brain

• Ventricles

• Bone

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CT Scan BasicsCT Scan Basics• Introduced in 1974 by Sir Jeffrey Hounsfield.• The original “Siretom” Circa 1974

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CT Scan BasicsCT Scan Basics• A CT image is a computer-generated

picture based on multiple x-ray exposures taken around the periphery of the subject.

• X-rays are passed through the subject, and a scanning device measures the transmitted radiation.

• The denser the object, the more the beam is attenuated, and hence fewer x-rays make it to the sensor.

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CT Scan BasicsCT Scan Basics• The denser the object, the whiter it is on CT

– Bone is most dense = + 1000 Hounsfield U.

– Air is the least dense = - 1000H Hounsfield U.

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CT Scan Basics: WindowingCT Scan Basics: Windowing

Focuses the spectrum of gray-scale used on a particular image.

2 Sheet Head CT

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•Brainstem•Cerebellum•Skull Base

–Clinoids–Petrosal bone–Sphenoid bone–Sella turcica–Sinuses

Posterior FossaPosterior Fossa

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CT ScanCT Scan

CT ScanCT Scan

Sagittal ViewSagittal View

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CisternsCisterns

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CT ScanCT Scan

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Brainstem Lateral ViewBrainstem Lateral View

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2nd Key Level22ndnd Key Level Sagittal View Key Level Sagittal View

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Cisterns at Cerebral Cisterns at Cerebral Peduncles LevelPeduncles Level

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CT ScanCT Scan

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Suprasellar CisternSuprasellar Cistern

CT ScanCT Scan

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33rdrd Key Level Sagittal View Key Level Sagittal View

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Cisterns at High Mid-Brain LevelCisterns at High Mid-Brain Level

CT ScanCT Scan

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VentriclesVentricles

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CSF ProductionCSF Production• Produced in choroid plexus in the

lateral ventricles Foramen of Monroe IIIrd Ventricle Acqueduct of Sylvius IVth Ventricle Lushka/Magendie

• 0.5-1 cc/min• Adult CSF volume is approx. 150 cc’s.• Adult CSF production is approx. 500-

700 cc’s per day.

CT ScansCT Scans

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Trauma PicturesTrauma Pictures

PATHOLOGYPATHOLOGY

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BB is for Blood is for Blood• 1st decision: Is blood present?

• 2nd decision: If so, where is it?

• 3rd decision: If so, what effect is it having?

BB is for Blood is for Blood

• Blood becomes hypodense at approximately 2 weeks.

•Blood becomes isodense at approximately 1 week.

• Acute blood is bright white on CT (once it clots).

BB is for Blood is for Blood

• Blood becomes hypodense at approximately 2 weeks.

• Blood becomes isodense at approximately 1 week.

• Acute blood is bright white on CT (once it clots).

BB is for Blood is for Blood

• Blood becomes hypodense at approximately 2 weeks.

• Blood becomes isodense at approximately 1 week.

• Acute blood is bright white on CT (once it clots).

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Epidural HematomaEpidural Hematoma

• Lens shaped

• Does not cross sutures

• Classically described with injury to middle meningeal artery

• Low mortality if treated prior to unconsciousness

( < 20%)

CT ScanCT Scan

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CT ScansCT Scans

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Subdural HematomaSubdural Hematoma• Typically falx or sickle-

shaped.• Crosses sutures, but does

not cross midline.• Acute subdural is a marker

for severe head injury. (Mortality approaches 80%)

• Chronic subdural usually slow venous bleed and well tolerated.

CT Scan CT Scan

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CT ScanCT Scan

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Subarachnoid HemorrhageSubarachnoid Hemorrhage

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Subarachnoid HemorrhageSubarachnoid Hemorrhage• Blood in the cisterns/cortical gyral surface

– Aneurysms responsible for 75-80% of SAH– AVM’s responsible for 4-5%– Vasculitis accounts for small proportion (<1%)– No cause is found in 10-15%– 20% will have associated acute hydrocephalus

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• 98-99% at 0-12 hours

• 90-95% at 24 hours

• 80% at 3 days

• 50% at 1 week

• 30% at 2 weeks

Depends on generation of scanner and who is reading scan.

CT Scan Sensitivity for SAHCT Scan Sensitivity for SAH

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CT ScanCT Scan

52

CT ScanCT Scan

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Intraventricular/Intraventricular/Intraparenchymal Intraparenchymal

HemorrhageHemorrhage

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CT ScanCT Scan

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CC is for CISTERNS is for CISTERNS

• 4 key cisterns– Circummesencephalic

– Suprasellar

– Quadrigeminal

– Sylvian

((BBlood lood CCan an BBe e VVery ery BBad)ad)

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CisternsCisterns• 2 Key questions to answer regarding

cisterns:– Is there blood?

– Are the cisterns open?

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BB is for is for BBRAINRAIN((BBlood lood CCan an BBe e VVery ery BBad)ad)

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TumorTumor

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AtrophyAtrophy

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AbscessAbscess

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Hemorrhagic ContusionHemorrhagic Contusion

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Mass EffectMass Effect

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StrokeStroke

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Intracranial AirIntracranial Air

Intracranial AirIntracranial Air

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Intracranial AirIntracranial Air

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VV is for is for VVENTRICLESENTRICLES((BBlood lood CCan an BBe e VVery ery BBad)ad)

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Ex-Vacuo PhenomenonEx-Vacuo Phenomenon

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BONEBONE

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Three StoogesThree Stooges

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If no blood is seen, all cisterns are present and open, the brain is symmetric with normal gray-white differentiation, the ventricles are symmetric without dilation, and there is no fracture, then there is no emergent diagnosis from the CT scan.

Blood Can Be Very Bad

RIPRIP

QuestionsQuestions

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Andrew D. Perron, MD, FACEPAndrew D. Perron, MD, FACEP

perroa@mmc.org(207) 662-7015207) 662-7015

Andrew D. Perron, MD, FACEP